Wavefront technique developed by the National Aeronautics and Space Administration (NASA) was initially applied in the field of space technology. Astronomers use wavefront analysis to process aberrations produced by the atmosphere in order to obtain relatively accurate data and images of the Galaxy. At present, this epochal technique is applied in the field of human vision measurement. Light entering the eye has to pass through several structures before arriving eventually at the retina to form visual images. However, refractive index and structure of the eye varies. Shapes of these structures also affect the propagation path of light entering the eye. Due to these and other factors, the so-called “high-order aberrations” occur.
Where parallel light enters a normal eye with perfect diopter behavior, reflective light and incident light reflected from the retina of the eye are parallel light and thus sharp images are formed. Upon entry of parallel light into the eye with aberrations, the wavefront of the light reflected from the retina may be distorted due to irregular structures of the eye, causing images to be blurred, scattered, dragged and etc. Where an eye examination is conducted with a wavefront high-order aberrometer, the wavefront high-order aberrometer uses wavefront data of the light reflected from the retina to calculate variations between optical paths, calculate the average inconsistency or errors of the optical paths up to the retina, describes the degree of diffusion of a light spot, precisely carry out detection and measurement of the cornea, lens, vitreous body, retina, and others, perform integrated analysis and measurement of various factors affecting the diopter of the eye, illustrate the status of the eye with a three-dimensional drawing, and precisely measure individual parts of the cornea. The related art is disclosed in U.S. Pat. Nos. 5,777,719 and 6,582,079.
An eye wavefront measuring device disclosed in the U.S. Pat. No. 5,777,719 corrects aberrations, using an adaptive optical element, such as a deformable mirror. Elements of this kind, designed mostly in the past to correct aberrations of astronomical telescopes, are characterized by considerable aberration correction and high response speed. However, such elements do have their own disadvantages, namely bulky and expensive, thus failing to meet the need for miniaturization and popularity of the eye aberration measuring devices.
In an attempt to solve the problems of the above patent, U.S. Pat. No. 6,582,079 suggests that an adaptive element for correcting aberrations can be replaced with a micro-machined reflector or a liquid crystal phase-compensating element. The overall size and price of the proposed device can be reduced because of the element. However, this kind of wavefront measuring device does not optimize measurement and correction, resulting in great uncertainty of aberration measurement. In addition, a target object seen by an eye undergoing measurement and the optical path of the measuring device are independent of each other, and thus the difference of optometric parameters before and after aberration correction cannot be accurately determined.
Laser surgeries nowadays, whether it is Laser in Situ Keratomileusis (LASIK) or Nidek Advanced Vision Excimer Laser System (NAVEX), employ not only simple eyeglasses-fitting or correcting techniques but also several kinds of high-order instruments to measure data related to eyesight problem, such as 3-D eye auto-tracing system, iris positioning system, flying spot scanning and wavefront high-order aberration analyzers. Among them, the wavefront high-order aberration analyzer is most important to correction of eyesight, because surgery is performed with a laser-cutting instrument based on data collected from the wavefront high-order aberration analyzer. Accordingly, the accuracy of measurement is very important.
Normally, lower-order aberrations and higher-order aberrations account for approximately 85% and 15% of the refractive errors of a bad eye respectively. According to Frits Zernike, a Dutch mathematician, aberrations are classified and divided into twenty Zernike orders. The lower orders, which include the first order and second order, are related to well-known eyesight problems of myopia, astigmatism and focus. Those higher than the third order are collectively called higher-order aberrations, including coma, spherical aberration and trefoil, etc. Traditional laser-based myopic surgery only reduces lower-order aberrations by 85%. However, for a person with higher-order aberrations, even if s/he regains a visual acuity of 1.0 to 1.2 after the laser surgery, the remaining 15% higher-order aberrations will remain unsolved, and thus s/he may still experience pro-operational sequelae, such as halo, glare, dazzle, and diplopia.
Wavefront aberration analysis is presently designed to evaluate eyesight only and has disadvantages, such as low repetition of measurement and inconsistent measurement results between different brands of instruments; in consequence ophthalmic surgeons resort to clinic experience instead of instrument-generated data, thus increasing the risks of surgery. Furthermore, pre-operational and post-operational visional changes cannot be assessed by means of wavefront measuring devices nowadays, thus increasing the uncertainty of the aforesaid surgery.
Accordingly, there is an urgent need to provide a measuring method and the device thereof for solving the drawbacks of the prior art, reducing the risks of wavefront laser scanning refractive surgery, and performing eye aberration measurement and correction precisely.